Analytical ultracentrifugation is the method of choice for determination of mass and shape of macromolecular complexes in solution. With over 30 years of literature on the technique, the method is well established. In recent years, advances in the instrumentation and data analysis software have made the method generally more accessible. The study of molecular interactions has gained a new popularity in the past few years as a logical next step to genomic and proteomic studies. The Hartwell Center, a biotechnology and bioinformatics core facility at St. Jude Children's Research Hospital (SJCRH), is seeking to expand its molecular interactions capabilities to meet the requirements of the Hospital's research programs. Understanding the composition and structure of multi-protein and protein-DNA complexes is a major part of this effort. We have identified five major research programs underway at SJCRH with immediate need for this technology. These research programs cover a broad range of studies including Immunology, Infectious Disease, Pharmacology, Pharmacodynamics, and Structural Biology. There are many other programs that have similar needs or will have in the near future. Currently, this technology is not available at SJCRH or in the city of Memphis. This application seeks funding for the purchase of an analytical ultracentrifuge to support these NIH-supported research efforts. The instrument will be incorporated into the Hartwell Center for Bioinformatics and Biotechnology at St. Jude Children's Research Hospital for present and future needs in basic biomedical research. [unreadable] [unreadable]